<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        class Person{
            static instance = null ; 
            constructor( name , age ){
                if(!Person.instance){
                    Person.instance = this ; 
                } else {
                    return Person.instance ;
                }
                this.name = name ; 
                this.age = age ;
            }
        }
        let zhangSan = new Person("张三",20);
        let liSi = new Person("李四",25);
        console.log(zhangSan); 
        console.log(liSi);
    </script>
</body>
</html>